The present invention relates to a jig used for forming a fiber-reinforced composite structure, as well as to a method for forming a fiber-reinforced composite structure using the jig. More particularly, the present invention relates to a jig comprising a combination of elastic jigs and rigid jigs and repeatedly usable for the formation of a fiber-reinforced composite structure in excellent dimensional and positional accuracy, as well as to a method for forming a fiber-reinforced composite structure using the jig.
Because fiber-reinforced composites are light in weight and have high strength, they are widely used for various structural members of automobiles, vessels, aircraft, etc. Fiber-reinforced composite structures are usually formed by impregnating a woven fabric of reinforcing fibers with a thermosetting or thermoplastic resin to form a plurality of prepregs, laminating the prepregs on a forming plate of a predetermined shape to form a preform, and subjecting the preform to pressurization and heating using a pressurizing bag. The preform, however, is likely to be deformed owing to fluidization of the resin in the preform during the above process if the preform has a complex shape, resulting in low dimensional and positional accuracy in the formed fiber-reinforced composite structure, particularly on the pressurizing bag side.
Hence, it is being attempted to make uniform the pressure applied by the pressurizing bag and improve the dimensional accuracy of the formed composite structure by placing an auxiliary forming member made of an elastomer (e.g. a silicone rubber), on the pressurizing bag side of the preform. However, because the elastomer is soft, it is necessary to use, in combination with the auxiliary forming member, a large positioning jig made of a metal in order to obtain high positional accuracy. Further, because the auxiliary forming member made of an elastomer tends to shrink owing to its chemical reaction with the epoxy resin, etc. in the preform and also the pressurization and heating applied during the forming process, the once-used auxiliary forming member has a shape not compatible with the positioning jig, making impossible its repeated use.
Therefore, an object of the present invention is to provide a forming jig repeatedly usable for the formation of a fiber-reinforced composite structure in excellent dimensional and positional accuracy without using any large positioning jigs.
Another object of the present invention is to provide a method for forming a fiber-reinforced composite structure using such a forming jig.
As a result of intensive research in view of the above objects, the present inventors have found that by using a forming jig comprising a combination of elastic jigs and rigid jigs, there can be formed a fiber-reinforced composite structure constituted by a plurality of first fiber-reinforced composite preforms linearly arranged at given intervals, and one or more second fiber-reinforced composite preforms passing through gaps between two adjacent first fiber-reinforced composite preforms and intersecting a row of the first preforms, in excellent positional and dimensional accuracy. The present invention has been completed based on the finding.
Thus, the forming jig of the present invention used for forming a fiber-reinforced composite structure from a plurality of first fiber-reinforced composite preforms linearly arranged at given intervals, and one or more second fiber-reinforced composite preforms passing through the gaps between adjacent two first preforms and intersecting a row of the first preforms, comprises a combination of (a) elastic jigs engageable with intersections between a row of the first preforms and the second preforms, and (b) rigid jigs attachable to the first preforms and the second preforms in portions of these preforms other than the intersections. The constitution of this forming jig provides high forming accuracy without using any large positioning jigs.
The width of each elastic jig in the direction of arrangement of the first preforms is preferably slightly larger in a free state than when combined with the rigid jigs for the formation of a fiber-reinforced composite structure. Thus, the rigid jigs are in pressure contact with the elastic jigs owing to their elasticity, securing the relative positions of the first preforms and the second preforms. Further, even if the elastic jigs shrink in the forming process, repeated forming is possible at a high forming accuracy.
Also, the forming jig of the present invention is preferably used together with an auxiliary forming panel made of a fiber-reinforced composite and two or more fixing means for fixing the preforms on the auxiliary forming panel. Combined use of the elastic jigs and the rigid jigs can keep the relative positions of the first preforms and the second preforms at a high accuracy. Therefore, mere fixing of ends of the preforms onto the auxiliary forming panel with simple fixing means can secure the positional accuracy of all the preforms.
The elastic jigs are preferably made of a silicone rubber, and the rigid jigs are preferably made of aluminum. Also, buffer members are preferably attached to the rigid jigs.
In one preferred embodiment, the first preform constitutes frames of an airplane body, while the second preform constitutes stringers of an airplane body.
The method of the present invention for forming the above fiber-reinforced composite structure uses a forming jig comprising a combination of (a) elastic jigs engageable with the intersections of a row of the first preforms and the second preforms, and (b) rigid jigs attachable to the first preforms and the second preforms in portions of these preforms other than the intersections.